David wrote:
http://wiki.diyfaq.org.uk/images/a/a4/Fuse_Box.jpg

http://wiki.diyfaq.org.uk/images/4/4d/Other_Thing.jpg

http://wiki.diyfaq.org.uk/images/c/c9/RCCB_MCB.jpg

You've got a 40A breaker in the new CU - that's probably the shower.
Hopefully it's less than 9.2kW.
The 30A breaker, or one of the red-dot fuses, may be the cooker - even
if there's only an oven it's probably wired for a hob as well. The other
two are presumably ring socket circuits.
The white dot will certainly be the lights, and one of the blue will be
the old immersion heater circuit - probably via the time clock on the
right.
The other blue could be anything, though probably a single appliance. It
could feed a garage if there is one.

The RCD arrangement is a bit odd. If the bottom RCD feeds both boards
and is 30mA, then you've got no discrimination with the RCD in the
top-left board - the bottom one is working as a whole-house RCD, which
isn't to current standards as a trip will take out everything. If the
bottom RCD is 100mA time delayed, this is presumably a TT system with an
earth rod, and there's effectively no RCD protection on the fuseboard.
Alternatively the bottom RCD could just feed the old board, which isn't
ideal as there isn't one switch to turn everything off.

Mike